Combined low frequency and turnstile antennas



G. H. BROWN COMBINED Low FREQUENCY AND TURNSTILE ANTENNAS March 7, V1939.

Filed Feb. 18, 1937 2 RN@ mfr TW/ /fM M .K5 sFN Mm m Gttorneg Patented Mar. 7, 1939 COMBINED Lo-W FREQUENCY AND TURNSTILE ANTENNAs George H. Brown, Haddonfeld, N. J., assignor to Radio Corporation o'f America, a corporation of Delaware Application February 18, 1937, Serial N0. 126,327

7 Claims.

My invention relates to antennas. More specifically, my invention contemplates the combinationl of a broadcast antenna, such as an earthinsulated steel tower, and a high frequency turnstile antenna. I have employed the term turnstile to describe the antenna which is disclosed in my Patent No. 2,068,261, Serial No. 33,281, which was led July 26. 1935, entitled Transmitting antennas and assigned to the same assignee as the present application.

In my Patent No. 2,096,782, Serial No. 79,635, which was filed on May 14, 1936, and entitled Antennas, I have described an antenna system which employs an antenna which is divided into two or more sections which are coupled by means of tuned circuits. The function of the antenna, described in the second mentioned application, is to operate simultaneously for the radiation of two or more radio waves of different frequencies. The lower section of the antenna is operated at the higher frequency, While the two sections are combined to operate at the lower frequency. 'I'he tuned circuits which couple the two sections are designed to oier high impedance to currents of the higher frequency and very low impedance to currents of the lower frequency.

'Ihe present invention diiers from the immediately preceding system in that a turnstile antenna is conductively connected to an insulated broadcasting antenna. The turnstile antenna is operated to radiate horizontally polarized high frequency waves throughout a circular eld while the broadcast antenna, in combination with the turnstile antenna, is used to radiate vertically polarized low frequency waves.

One of the objects of my invention is to provide improved means for radiating a high frequency wave and a low frequency wave from a common antenna structure.

Another object is to provide means for combining an antenna for radiating horizontally polarized high frequency waves with an antenna for radiating vertically polarized low frequency Waves.

A further object is to arrange a turnstile antenna and a broadcast antenna to provide a combined antenna structure in which the high frequency horizontally polarized waves are radiated from a turnstile which isconductively secured to the broadcast' antenna and at least a portion thereof is used for the radiation of the low frequency waves.

My invention may be best understood by referring to the accompanying drawing in which (Cl. Z50-33) Figure 5 is a circuit diagram showing the I,

method of connecting the turnstile antenna.

In Fig. 1 a conductive antenna structure I is insulated from ground by insulators 3. The antenna is suitably connected to a transmitting apparatus (not shown) by means of lead 5. A conductive mast 1 is mounted on the top of the anf tenna structure. At intervals of one-half wave length, a plurality of conductive Aelements 9 are horizontally fastened to the mast l. The conductive elements 9 are preferably a half wave length long. The mast 'l and two sets of conductor eleu ments 9 and l0, arranged in 90 relation, form a turnstile antenna which is energized by currents at the desired high frequency.

The elements 9 of the turnstile antenna are fed by a pair of transmission lines. One such pair I I is shown as extending through the central portion of the antenna I. The transmission line conductors are connected to one set of antenna elements 9 at approximately one-twentieth of a wave length from the surface of the mast l. The transmission line is transposed between antenna elements 9 so that the currents in a set of elements in the same plane are all in the same phase. The currents in the antenna elements I0 which are disposed at right angles to the elements l 9 are fed by a similar transmission line but in a phase relation with respect to the currents in the first-mentioned set of antenna elements 9. The 90 phase and special relationship establishes a circular rotating iield.

Fig. 3 illustrates an antenna structure I3 of substantially square cross section which is insulated from earth by insulators I5. 'I'he antenna is connected to a transmitting apparatus (not shown) by lead I1. The turnstile antenna sections I9 are connected directly to the antenna structure I3. The antenna elements I9 are spaced at intervals of one-half wave length and are preferably about one-half Wave length long. It is understood that the antenna elements I9 are arranged in one plane and a similar set of elements 20 are arranged in a second plane which is disposed 90 with respect to the first plane. The turnstile antenna is fed by means of transmission lines 2| which may be positioned external to the antenna structure I3 as shown, or, if desired, may be placed within the antenna structure. The transmission lines 2l are connected to the antenna elements I9 in accordance with the arrangement previously described in connection with Fig. 1.

In order to prevent the high frequency currents in the turnstile section of the antenna from entering the low frequency section of the antenna, it is necessary to include a suitable network in the transmission lines which connect the transmitting apparatus to the turnstile antenna. One

suitable circuit is shown in Fig. 5. The turnstile antenna elements 23 and 25 have been respectively labeled E-W and N-S to indicate a 90 relationship with respect to the points of the compass. While single antenna elements 23 and 25 have been shown, in practice a plurality of elements are used as shown in Figs. 1 and 2.

The transmission lines 2l which are connected to the antenna 23 include inductors 29, 3l and capacitors 33. It will be observed that the inductors and capacitors are symmetrically arranged with respect to the transmission line 2l. 'Ihe turnstile antenna element 25 is fed by means of a transmission line 35 which includes inductors 31 and 39 and a capacitor 4 l. The inductors and capacitors 39 and 4I are also symmetrically arranged with respect to the transmission line 35. The function of the inductors 29 and 3l is to suitably match the transmission lines to prevent the establishment of standing waves. The inductors 29 and 31 may be replaced by stub sections' of transmission line.

The network comprised of inductor 3l and ca.- pacitors 33 and the network comprised of capacitor 4| and inductors 39 are used to obtain a quadrature relationship between the currents which are fed to the turnstile antenna elements 23 and 25 and also to properly terminate the transmission line which is connected to the high frequency transmitting apparatus. The junction of these twor networks is connected to a transmission line 43. Each of the wires of this transmission line includes filter networks which are comprised of inductors 45 and capacitors di. These filters are parallel resonant to the low frequency currents which tend to flow in the transmission line 43 to the high frequency transmitter. A stub section 49 is connected across the line and to ground 5I to effectively ground the transmission line 43 for low frequency currents. The stub section is tuned to a quarter wave length with respect to the high frequency currents so that it offers very high impedance to these currents and very low impedance to the low frequency currents. 'I'he transmission line i3 is suitably connected to the high frequency transmitter which has not been shown.

Thus, I have described a low frequency antenna which is used to radiate low frequency iields in combination with a turnstile antenna, which is used to radiate high frequency fields of substantially circular pattern. A suitable filter system has been described which prevents the high frequency currents in the turnstile antenna from entering the low frequency system and vice versa.

I claim as my invention:

1. An antenna system including in combination a low frequency antenna and a high frequency antenna, said low frequency antenna having the characteristic of radiating vertically polarized waves and said high frequency antenna having the characteristic of radiating horizontally polarized high frequency waves, and further characterized by a common connection between said antennas for low frequency currents.

2. An antenna system including in combination a low frequency antenna and a. high frequency antenna., said low frequency antenna having the characteristic of radiating vertically polarized waves and said high frequency antenna having the characteristic of radiating horizontally polarized high frequency waves, and further characterized by the use of at least a portion of the high frequency antenna for the establishment of the low frequency radiation.

3. An antenna system including in combination a low frequency antenna and a high frequency antenna, said low frequency antenna having the characteristic of radiating vertically polarized waves and said high frequency antenna having the characteristic of radiating horizontally polarized high frequency waves, and further characterized by the conductive connection of both the low and high frequency antennas.

4. An antenna system including in combination a low frequency antenna and a high frequency antenna, said low frequency antenna having the characteristic of radiating vertically polarized waves and said high frequency antenna having the characteristic of radiating horizontally polarized high frequency waves, and further characterized by the high frequency antenna being located on the top of the antenna structure and electrically connected thereto.

5. An antenna system including a first antenna structure which is adapted for being energized by low frequency currents, a second antenna structure which is adapted for being energized by high frequency currents, and means conductively and mechanically connecting said first and second antenna structures whereby said first and second antenna structures are energized by said low frequency currents.

6. An antenna system including a iirst antenna structure which is adapted for being energized by low frequency currents, a second antenna structure which is adapted for being energized by high frequency currents, and means conductively and mechanically connecting said first and second antenna structures whereby said first and second antenna structures are energized by said low frequency currents, said high frequency antenna being characterized by its adaptability for the radiation of horizontally polarized waves, and said low frequency antenna being characterized by its adaptability for the radiation of vertically polarized waves.

7. An antenna system including a rst antenna. structure which is adapted for being energized by low frequency currents, a second antenna structure which is adapted for being energized by high frequency currents, and means conductively and mechanically connecting said first and second antenna structures whereby said first and second antenna structures are energized by said lo-w frequency currents, said high frequency antenna including a plurality of crossed antenna elements and means for feeding high frequency 4currents thereto for establishing a radiated field of substantially circular pattern.

GEORGE H. BROWN. 

